There are many types of road surfacing and drainage (eg, inslope with ditches, outslope, dips or other diversions at varying frequencies). Roads can capture runoff into the catchment, or move it to another. Some roads develop wheel tracks that divert flow. Walking or driving roads can help identify diversions, culverts, etc. Using location app. with Ipad and free Avenza software may help locate drainage features. Remotely, LiDAR is also a valuable tool to help define drainage from roads or also in areas with low gradient topography. Normally roads run through, across or intersect drainage catchments or watersheds. I suppose, in some instances, roads have extended lengths before any cross drainage, the ditches therefore erode deeply into the landscape and essentially define a stormwater tributary or catchment. How permeable the road surface, prism, construction methods (such as compaction) and materials, adjacent soils, topography form are added considerations. Roads built with adequate BMP drainage have frequent diversions into adequate filter zones would have a different stormwater footprint from poorly designed and maintained roads. Where roads are less that 5% of the rural landscape are generally going to have a much smaller effect in modelling than in urban areas where roads may be 25% or more of the surface. Since you are studying this, and working with models, you might try both ways - ie, designating road catchments and not, determining surface catchments vs surface catchments modified by road capture into or diversion out of Catchment.

Sure you can.